Manipulation and control of the amounts and types of cellulose and lignin synthesized and deposited in plants and trees is of interest in the forestry, paper and biofuels industries. Tree species synthesize large quantities of lignin, particularly in and around the vascular tissues. Manipulating lignin and/or cellulose in plants and trees can prove beneficial by providing trees and plants with improved disease resistance, increased strength for use in construction, increased biomass usable as fuel or biofuel, improved digestibility (such as for forage crops), as well as having qualitative and quantitative variation in cellulose and/or lignin for paper processing. However, progress in this area has been impeded by difficulties in regulating gene expression in transgenic plants in tissue- or cell-type specific manners.